I'm one of those guys who mainly comments.
I work long hours and I don't have much time. So for me I have to find the balance that makes most sense. I could spend my time writing posts that few people would see or I can spend it commenting on posts from authors I like.
This is the better option for me all around. More people see my comments than see my posts. I help add value to quality work. I make more from comments than I do for posts. That means that currently, me commenting is better for Steem, the authors, and myself.
This might change in the future if I have more time and as my SP increases but I can't really see me slowing down on commenting. If anything I will probably comment more.
Another factor I think about is that when I comment on a post my interests and the authors interests are aligned. We both derive satisfaction from acknowledgment and engagement in what we have written. I put effort into comments, just as authors put effort into posts. When others recognize that it makes it feel like our time wasn't wasted.